This invention relates in general to vehicle disc brake assemblies and in particular to controlled contact guide pins adapted for use in such a vehicle disc brake assembly.
Most vehicles are equipped with a brake system for slowing or stopping movement of the vehicle in a controlled manner. A typical brake system for an automobile or light truck includes a disc brake assembly for each of the front wheels and either a drum brake assembly or a disc brake assembly for each of the rear wheels. The brake assemblies are actuated by hydraulic or pneumatic pressure generated when an operator of the vehicle depresses a brake pedal. The structures of these drum brake assemblies and disc brake assemblies, as well as the actuators therefor, are well known in the art.
Typical disc brake assemblies include a rotor, a caliper, and an anchor bracket. The rotor is secured to the wheel of the vehicle for rotation therewith and includes a pair of opposed friction plates. The caliper includes a pair of brake shoes which are disposed on opposite sides of the brake rotor. The anchor bracket is attached to a non-rotatable component of the vehicle, such as the vehicle frame. The caliper is slidably supported on the anchor bracket by guide pins.
The brake shoes are connected to one or more hydraulically or pneumatically actuated pistons for movement between a non-braking position, wherein they are spaced apart from the opposed friction plates of the rotor, and a braking position, wherein they are moved into frictional engagement with the opposed friction plates of the rotor. When the operator of the vehicle depresses the brake pedal, the piston urges the brake shoes from the non-braking position to the braking position so as to frictionally engage the friction plates of the rotor and thereby slow or stop the rotation of the associated wheel of the vehicle.
Each of the guide pins has a stem that extends into the bore. The stem has a substantially circular cross section of constant diameter that may also include at least one flat portion on an exterior surface on the stem. The flat portion extends along a length of the guide pin, reduces a cross sectional area of the guide pin, and permits grease and air to escape the bore when the guide pin is inserted in the bore. For efficiency in producing the guide pin, a single flat portion may be provided. Alternatively, multiple flat portions may be evenly spaced around a circumference of the guide pin to efficiently permit the grease and air to escape. For example, three flat portions may be provided at 120° increments on the circumference of the stem. Otherwise, no particular orientation of the at least one flat portion is preferred or established relative to the bore.
The anchor bracket bores have a greater diameter than the guide pins. Thus, the guide pins have a clearance between the exterior surface of the guide pin and an interior surface of the bore such that the guide pins may move within the bores and contact the interior surfaces of the bores. However, such contact between the guide pins and the interior surfaces of the bores produces noise, vibration, and harshness for the disc brake assembly. Thus, it would be desirable to reduce or control metal on metal contact between the guide pins and the interior surface of the bores.